Disk-based storage devices such as hard disk drives (HDDs) are commonly used to provide non-volatile data storage in a wide variety of different types of data processing systems. In a typical HDD, data is recorded on tracks of a magnetic storage disk using a write signal comprising multiple write pulses. The write signal is generated by a write driver that is coupled to a write head of the HDD via a transmission line. In order to record a given data bit, the write driver generates a write pulse that transitions from a negative write current to a positive write current, or vice-versa.
At the completion of a given write operation, the write head may exhibit remanent magnetization after the write current has been turned off. This residual magnetization or “domain lock up” can be the cause of a phenomenon known as erase after write (EAW), where a non-energized (i.e., zero write current) head is seen to erase or degrade previously-written tracks of the disk. These previously-written tracks may comprise user data or even fixed servo sectors that are used to control the tracking of the radial position of the write head. In order to address the EAW problem, a degauss signal may be applied to the write head immediately after completion of the write operation.
The typical degauss signal waveform includes current pulses that repeat at a fixed frequency and decay in amplitude over time, usually from a write mode current level to a zero current level or other small final value. The degauss signal waveform is therefore typically an alternating current waveform, with pulse amplitudes decaying at a specified rate. The waveform may include overshoot on each pulse.